RESUMEN
One of the central focuses in self-assembly is precisely controlling the self-assembly pathway so that the target molecules can be produced exclusively. Trans-1,2-cyclohexanediamine contains two amino units that form a 60° angle when projected on a plane. This angle naturally favors the formation of triangular products in most cases when trans-1,2-cyclohexanediamine is used as a bisamino building block in the synthesis of macrocycles and tubes. Here, we synthesized a slightly bent tetraformyl precursor bearing a central dibenzothiophene moiety, whose 3,7-positions are functionalized with two m-phthalaldehyde units. We observed that combining this tetraformyl building block with trans-1,2-cyclohexanediamine yielded a quadrangular tube when the concentrations of the precursors were relatively high. Both experimental measurements and theoretical calculations indicate that the formation of this unlikely occurring quadrangular product was driven by the intramolecular C-H···π interactions between the dibenzothiophene building blocks within the tube framework. This driving force, however, was disturbed in the triangular tube, a smaller counterpart whose formation was considered previously much more thermodynamically favored. These results improved our fundamental understanding on how to create those products whose syntheses are considered difficult or impossible, by modulating the intramolecular driving forces.
RESUMEN
How Nature synthesizes enantiomerically pure substances from achiral or racemic resources remains a mystery. In this study, we aimed to emulate this natural phenomenon by constructing chiral tetrahedral cages through self-assembly, achieved by condensing two achiral compounds-a trisamine and a trisaldehyde. The occurrence of intercomponent CHâ â â π interactions among the phenyl building blocks within the cage frameworks results in twisted conformations, imparting planar chirality to the tetrahedrons. In instances where the trisaldehyde precursor features electron-withdrawing ester side chains, we observed that the intermolecular CHâ â â π forces are strong enough to prevent racemization. To attain enantioselective self-assembly, a chiral amine was introduced during the imine formation process. The addition of three equivalents of chiral amino mediator to one equivalent of the achiral trisaldehyde precursor formed a trisimino intermediate. This chiral compound was subsequently combined with the achiral trisamino precursor, leading to an imine exchange reaction that releasing the chiral amino mediator and formation of the tetrahedral cage with an enantiomeric excess (ee) of up to 75 %, exclusively composed of achiral building blocks. This experimental observation aligns with theoretical calculations based on the free energies of related cage structures. Moreover, since the chiral amine was not consumed during the imine exchange cycle, it enabled the enantioselective self-assembly of the tetrahedral cage for multiple cycles when new batches of the achiral trisaldehyde and trisamino precursors were successively added.
RESUMEN
Two triangular prismatic cages were synthesized by combining a trishydrazide and two bisformyl precursors in strongly acidic water, where the dynamic nature of hydrazone was turned ON. An anionic guest was used as the template to drive the cage formation. Performing counterion exchange removed both the template and the Brønsted acid. The removal of the latter afforded the cages' kinetic inertness by turning OFF the reversibility of hydrazone. The cages can thus be used for recognizing various guests in water without observable degradation, driven by the hydrophobic effect. Upon being accommodated within the cage cavities, an anthracene derivative was protected from UV-stimulated oxidation, which would occur otherwise in the bulk solution without the protection from the host.